Embodiments of the invention relate to a control system for a subsea well.
A control system for a subsea well, for example a hydrocarbon production well, generally comprises a subsea tree and a tubing hanger which carries production tubing. In the tubing, there is a downhole safety valve (DHSV), typically in the form of a so-called hydraulically operated surface controlled subsurface safety valve (SCSSV). When hydraulic pressure is applied via a control supply line, the DHSV opens against the action of a spring or production fluid pressure. In the event of a failure in the control system, supply of fluid for opening the DHSV is stopped, resulting in closure of the DHSV under the action of the spring or production fluid pressure, to prevent the flow of production fluid from the well.